Acetic acid is a major metabolic product of certain bacteria which decompose complex organic materials under aerobic conditions. In various natural microbial ecosystems and in those used by man for waste treatment, the strictly anaerobic microorganism Methanosarcina barkeri is of major importance for subsequent conversion of acetic acid to the gaseous products carbon dioxide and methane. The enzymes involved in this metabolic conversion of acetate are under study in this project and detailed information about this process is beginning to emerge. Research on the initial acetate carbon-carbon bond cleavage event is centered on studies of the enzyme carbon monoxide dehydrogenase (CODH), since it has been implicated to be the primary acetate carbonyl group insertion/excision catalyst. Methyl group transfer steps are subsequently involved prior to methane formation. Previously this project yielded a detailed comparison of structural and catalytic properties of two separate methyltransferase enzymes, one of these predominates in cells grown on methanol and the other is prevalent in cells metabolizing acetate. A detailed physicochemical study has also been made of highly purified CODH. Studies have been conducted on the structural and enzymatic properties of a high molecular mass protein complex containing CODH and corrinoid protein components. It was discovered that the isolated complex per se catalyzed acetyl-CoA decomposition. In this reaction the natural methyl group acceptor tetrahydrosarcinapterin was required as a co-substrate. Reaction products and stoichiometry have been established.